<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        /* 标签选择器 */
        h1{
            text-decoration: line-through;
        }
        /* id选择器 */
        #title1 {
            text-decoration: underline;
        }
        /* 类选择器 */
        .good {
            color: brown;
        }
        /* 通配符选择器：覆盖浏览器默认样式 */
        *{
            text-align: center;
        }
        /* 伪类选择器 */
    </style>
</head>
<body>
    <h1>早上好</h1>
    <h2 id="title1">早上好</h2>
    <h3 class="good">早上好</h3>
</body>
</html>